The present invention relates to a clamping device suitable for clamping a work piece to be machined.
In order that the work piece is machined by a machine tool, it is necessary either to fix the work piece on the table of the machine tool in a precise and firm manner, or to mix the work piece on a work pallet in a precise and firm manner before the work pallet is secured to the machine tool table or the pallet. Various types of such clamping devices suitable for fixing work pieces to be machined have been proposed and put to actual use.
For example, a clamping device shown in FIG. 34 is at present in wide use, which clamping device 101 is placed on the base surface of the table or pallet so as to clamp a work piece WK in conjunction with an reaction receiving device 102. The clamping device 101 includes a clamp main body 103, clamp member 104 (input/output member), and a leg member 106 inserted in a T-shaped groove 105 formed on a base surface 100.
The clamp main body 103 has a reaction support 107 provided in the rear end portion thereof, and having an inclined face 108 on its front end. The clamp member 104 has a rear end portion including a rear end face 109 abutting the inclined face 108. The clamp main body 103 is fastened by means of a bolt 110 and leg member 106, and the clamp member 104 is arranged such that it may be driven downward by a clamp bolt 112 inserted from above into a bolt hole 111 of the clamp member 104. The clamp member 104 has an output portion 113 formed in its front end portion, and is biased upwardly by a spring 114.
The reaction receiving device 102 includes a main body block 115, a leg member 116, and two bolts, 117. The main body block 115 is fastened on the surface 100 by threadedly connecting two bolts 117 with the leg member 116.
As illustrated, before setting of the work piece WK in position, the bolt 112 is loosened to the extent that the clamp member 110 may be raised to a certain level. The work piece WK is then placed in position. Next, when the bolt 112 is fastened, the rear end face 109 of the clamp member 104 is guided by the inclined face 108 to allow the clamp member 104 to travel in a forward direction with the result that the work piece WK can be rigidly clamped between the output portion 113 of the clamp member 104 and a reaction output portion 118 of the main body block 115. In the alternative, the inclined face 108 may have a dovetail groove, and the rear end face 109 of the rear end of the clamp member 104 may be provided with a corresponding engaging portion for engaging with the dovetail groove.
Recent machine tools have been improved remarkably in their performance, and their machining accuracy has considerably improved. However, in conventional clamping devices, the arrangement is essentially such that the clamp member is advanced for clamping as it is lowered by fastening a bolt. Therefore, it is difficult to move the clamp member only forward and backward, and it is difficult to restrict assuredly the vertical movement of the clamp member. As, there exists a gap between the clamp member and the clamp main body which permits the downward movement of the clamp member, the bolt hole is of an elongated type, and an upward-directed component is included in a reaction force on the clamp member from the inclined face, when work piece is subjected to a strong cutting force, the clamp member will repeat a minute up-and-down movement so that the work piece is liable to float off the clamp main body, thus causing an error in the machining accuracy.
In addition, as another disadvantage, because the clamp member moves downward when clamping through the tightening of the bolt, scratching damages due to the output portion are caused on the surface of the work piece, and therefore clamping of the finished part of the work piece is not desirable. And, since the output portion of the clamp member is formed integral with the clamp member, the output portion cannot be exchanged for another one to fit to the configuration of a work piece. The aforementioned disadvantages cause various inconveniences to practical use.